GAR transformylase, which is responsible for the incorporation of formate carbon into what becomes position 8 of the purine ring, has been completely separated from 5-amino-4-imidazolecarboxamide ribotide transformylase (3). The latter enzyme is responsible for the incorporation of formate carbon into position 2 of the purine ring. The requirement for folic acid compounds has been demonstrated in both reactions of purine biosynthesis involving formate incorporation (4-7).